This paper presents the design and fabrication of 3D printed WR-28 waveguide horn antennas operating in the Ka-band frequency range between 26.5GHz and 40GHz. Three antennas are fabricated from polylactide acid filaments in conductive and non-conductive variants; the latter is covered with conductive paint. The gain and voltage standing wave ratio performance of the fabricated horn antennas is measured, showing promising performance. Antenna gain values between5dBi and 14 dBi are found, comparable to the performance of metal milled horn antennas.